1. Field of the Invention
This invention generally relates to an optical subassembly, and more particularly to a factory-settable optical subassembly used in an optical transceiver module.
2. Prior Art
The efficiency of an optoelectronic converter in an optical transceiver module is one of the most important factors in optical transmission systems. It depends on both the efficiency of a laser diode receiving light from an optical fiber and a laser device transmitting light into the optical fiber.
A conventional optical subassembly of a transceiver module usually comprises a metal top can, a metal base cover, and a laser device. The top can attaches to the base cover to enclose the laser device. The top can comprises a locating means for positioning a ferrule of an optical connector inserted therein, and the laser device comprises a lens to focus light on an end surface of the ferrule. However, each top can of the conventional optical subassembly can only efficiently focus one wavelength of light, since the top can fixes only one distance between the lens and an end of the ferrule. This distance and the lens characteristics determine which wavelength will be efficiently transmitted. Other will not focus. Therefore, different top cans will be needed to transmit different wavelengths of light into the end surface of the ferrule. Manufacturing such a plurality of different top cans having different dimensions would be expensive.
In order to solve the above mentioned problems, US. Pat. No. 5,631,991 discloses an improved optical subassembly. The optical subassembly comprises a cover, a laser means, and a lens. The cover has a top section and a bottom section in communication therewith. The top section comprises a fastener for securing a ferrule inserted therein and the bottom section receives the laser means and the lens. The lens can move in the bottom section along a direction of an axis of the cover. When different wavelengths of light are transmitted from the laser means to the optical fiber, the distance between the lens and the end surface of the ferrule can be adjusted by positioning the lens at an appropriate position so that light can properly focus on the end surface of the ferrule. Maximum optical power is thus obtained. However, the lens is susceptible to being damaged or optical characteristics of the lens are susceptible to being degraded during such an adjustment due to improper manipulation, which in turn can lead to decrease optical efficiency.